On 2023-11-16 19:35, Guy Harris wrote:
On Nov 16, 2023, at 6:29 PM, Paul Eggert <eggert@cs.ucla.edu> wrote:
...which means that the phrase "Daylight Savings Time" in the POSIX standard refers to something that's not exactly the same as "daylight saving time" as generally understood, i.e. it doesn't necessarily mean "the time that's in effect during summer and possibly some close-to-summer dates in spring and autumn, if clocks are adjusted twice a year, with the clock setting during summer and blah blah blah being ahead of the clock setting during the rest of the year".
If you're accustomed to the United States then that's indeed what "daylight saving time" has meant. And given the US's influence it's not surprising that the usage is common elsewhere. However, it's not universal, and POSIX and TZDB support the more-general case. The earliest use of negative DST that's recorded in TZDB is Czechoslovakia during winter 1946/1947. That's also the earliest use recorded in the Wikipedia page on negative DST <https://en.wikipedia.org/wiki/Winter_time_(clock_lag)> - a page that you've edited. I would not be surprised if negative DST was used somewhere even before 1946 but we don't know about it, as records before 1970 are so woefully incomplete.